As gaskets for use in internal combustion engines, there have heretofore been known in the art steel type gaskets in which the metallic sheets are laminated with one another, gaskets comprising steel type gaskets coated with rubbers or synthetic resins, asbestos gaskets comprising asbestos, and flexible graphite sheets comprising expanded graphite in the form of sheet.
In metallic gaskets, such as steel type ones, originally having low percent recovery after compression, however, a work called "beat-standing" is carried out on the portions thereof for enhancing their sealability so that a recovery force necessary for sealing may be obtained on the worked portions. However, the beats tend to be fatigued during a prolonged period of service time, and thus, the metallic gaskets will raise a problem that their sealability are not relied upon. Further, since the metallic gaskets are constituted of metallic sheets, processes for the manufacture thereof are complicated and the gaskets so manufactured are expensive.
Coating materials consisting only of rubber or a synthetic resin serves only to make up for surface irregularities of a mating material to be coated therewith, and thus, coats made from said coating materials are not heat resistant enough to cope with high load and temperature of engines. When they are used in the preparation of gaskets, the resulting gaskets will not have satisfactory sealability.
Japanese Patent Publication Gazette No. 53-44917 discloses a flexible graphite sheet material having Teflon added thereto. The disclosed sheet will exhibit excellent properties when used in preparing a gasket. However, in order that the disclosed sheet is to be used in preparing a gasket it should naturally has a thickness of at least 0.3 mm, usually at least 0.4 mm. It is difficult to supply such thick graphite sheets at low costs.
Japanese Patent Publication Gazette No. 57-25383 discloses a carbon-metal composite material comprising a metallic sheet having a sheet of expanded graphite adhered to one or both surfaces thereof, the composite material being excellent in anti-corrosive and impermeable properties. But it is not a material for use as a gasket in internal combustion engines.
Japanese Utility Model Publication Gazette No. 62-24029 discloses a gasket for a cylinder head, comprising a lead plate as the coat layer. The disclosed gasket, however, does not have satisfactory sealability because of its low recovery force after compression.
Recently, there are proposed gaskets comprising aramid fibers and synthetic resins. While such gaskets have a satisfactory sealability, they pose problems in low heat resistance and high manufacturing costs.
The invention is to solve the above discussed problems associated with the prior art. Thus, an object of the invention is to provide a gasket for use in internal combustion engines in which the demerits of metallic gaskets are made up for by the merits of expanded graphite sheets and which has improved gasket properties such as high recovery from compression, a satisfactory friction coefficient and good stress relaxation rate, leading to an excellent sealability and which can be prepared at a lower cost by using a simple manufacturing step of coating or printing than the conventional gaskets where preformed sheets of expanded graphite are used.